你可以有一个按钮来触发消息。Firebase Auth文档指定verifyPhoneNumber()方法有四个不同的回调，其中一个是codeSent。这个回调可以用来将用户导航到第二个屏幕。
就像这样：

FirebaseAuth auth = FirebaseAuth.instance;

await auth.verifyPhoneNumber(
  phoneNumber: '+44 7123 123 456',
  codeSent: (String verificationId, int? resendToken) async { <- This will be executed when after the message is sent
    // here you'll navigate the users to the second screen! (you must pass the `verificationId` as a parameter to the following screen)
   
  },
);

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在另一个屏幕上...

FirebaseAuth auth = FirebaseAuth.instance;

 // you should have a method which will be called once the user entered the received code...

Future<void> logIn(String smsCode ) async { <- value entered by the user
    // Create a PhoneAuthCredential with the code
  PhoneAuthCredential credential = PhoneAuthProvider.credential(verificationId: widget.verificationId, smsCode: smsCode);
    
  //Sign the user in (or link) with the credential
  await auth.signInWithCredential(credential);
}

型
希望这对你有帮助！